In recent years, liquid crystal display devices are widely used as a display device of smartphones, tablet computers, vehicle-navigation systems, etc. In general, a liquid crystal display device comprises a liquid crystal display panel and a backlight unit overlaid on the rear surface of the liquid crystal display panel to illuminates the liquid crystal panel. The backlight unit includes a reflective layer, a light guide, an optical sheet, a light source unit, a case (bezel) in which these members are accommodated, etc. The light source unit includes a wiring substrate and a plurality of light sources, for example, light-emitting diodes (LEDs) mounted on the wiring substrate.
The wiring substrate of the light source unit is bent to a back side of the case and is electrically connected to a relay printed circuit board. Here, in some cases, the wiring substrate is electrically and mechanically jointed to the relay printed circuit board using solder. However, when jointed with solder, the soldered portion forms relatively tall solder bumps. These solder bumps can be an obstacle in thinning the back light device and the liquid crystal device.